The present invention relates generally to polymer components having a metallic coating on an exterior surface thereof. More specifically, the present invention relates to molded polymer components with a metallic layer on their exterior surface wherein the metallic layer is entirely formed within the mold cavity before the part is removed from the mold. Further, the present invention is directed to a method of forming a molded polymer part to include a metallic layer about its exterior surface while the part remains in the mold.
In the component manufacturing industry, it is highly desirable to form components using the fewest number of steps, thereby increasing the speed and efficiency while reducing the cost at which such parts can be produced. Given these goals, a popular manufacturing process for the formation of components is net shape molding. In the net shape molding process, a molten raw material is placed into a mold cavity such that when the component is removed from the mold it is in its finished form and no further processing is required to complete it. Due to the simplicity of the process, net shape molding is used in conjunction with a wide variety of base materials including polymer resins and various metals.
While the net shape molding process works well for a broad range manufactured components, the difficulty with using a net shape molding process, particularly with polymer materials, is that often other steps are required in order to impart various other desirable properties to the part after the molding step is completed. For example, parts that are utilized in electronic devices often must provide additional functionality such as transferring heat within the device, shielding against the effects of electromagnetic interference (EMI), reflecting radiant energy away from sensitive components within the device and/or reflecting light output such as that from a lamp or a light emitting diode (LED). Accordingly, in the prior art, when a reflective surface was desired, the part often was formed using another manufacturing method such as spinning or machining of metal components or by providing a metallized coating onto the desired surface of a polymer based part thereby requiring additional processing steps beyond the net shape molding process. In either case, the cost of manufacturing the part is dramatically increased.
The preferred method of metallizing a polymer component after it has been net shape molded has several drawbacks. Principally, as was stated above, metallizing dramatically increases the cost and time required to manufacture the part. Generally, metallizing requires that the part, once removed from the mold, be prepared using a chemical bath, subsequently plated using vapor deposition or vacu-plating and then finally clear coated to protect the thin layer of metal that was deposited onto the part. These additional steps introduce a great deal of additional handling of the part before it attains its finished state and result in nearly doubling the cost associated with manufacturing the part. Further, even though the cost of the part is increased dramatically, the coating is highly susceptible to wear, peeling, flaking and scratching, all of which lead to premature failure of the component.
Alternately, in the prior art when a part required enhanced thermally conductive properties, the base polymer resin was typically loaded with highly thermally conductive fillers to enhance the thermal conductivity of the finished part. Such fillers typically include carbon black, carbon fibers, ceramic powders and/or metal flakes. While the thermal conductivity of the polymer is improved by the addition of such fillers, the cost of these conductive fillers is typically quite high and the filler loadings that are typically required in order to attain the desired thermal and electrical conductivity properties also resulted in a dramatic impact on the flexibility and strength of the base polymer resin. Further, due to the difference in density between the filler materials and the polymer resin component, the molded part typically includes a resin rich region at its outer surfaces with a concentration of the filler materials towards the center of the component. This is particularly problematic when trying to increase the electrical conductivity of the part because electrical flux tends to travel over the surfaces of objects, precisely in the region of the part that has the lowest concentration of filler material. Accordingly, it is difficult to produce a part that has a relatively high electrical conductivity using net shape molded filler polymers.
Therefore, there is a need for a component that is formed during the molding process to include a metallized surface. There is a further need for a component that is formed during the molding process to include an integrally formed metallized surface that is highly durable and resistant to wear. There is still a further need or a process of in mold metallization of polymer components that preserves all of the desirable aspects of the net shape molding process and eliminates the additional steps that are traditionally associated with metallizing. Finally, there is a need for a compounded material that is suitable as feed stock for use in connection with the net shape molding of an in mold metallized polymer component.